You are forgetting Paypal fees which are another 3%. So, it's really about $36 in total fees on $300 which still leaves $64 in net profit assuming you are in a state with roughly 10% tax like California. Of course, it doesn't factor in your time, gas back and forth from wherever you bought the item from and to the post office, plus packing supplies and the risk that something could go wrong and you could end up eating the whole thing if a bidder complains for any reason. So, yes, you can make a little bit of money but it hardly seems like it's worth all the effort.
I sell on ebay to hopefully make just enough to pay for my gaming and it works out usually. I honestly don't think I've spent any of my actual job money on video gaming in a couple years now. I come close quite a bit but things have so far ended up working out to where I don't need to use my actual income. I'm not a big time reseller though either. I'm sure others probably make much more and do better with it than me.
Basically imo it is worth it in the long run if you know what you're doing. Sure sometimes things go wrong but so far I haven't ended up completely screwed on much. I ended up having to send one person a game twice so lost out on $100 or so on that.
Also it's very risky selling codes, Xbox codes particularly. I do it sometimes but wouldn't recommend it at all. I've been screwed a few times there since the type that buys those codes also happen to be douche bags...but other than that I haven't had any major problems.
As for gas money, you can do home pick up if you're shipping at least one item priority via USPS. No need to go to the post office. Not sure about other services but that's what I usually do.
Edited by ShockandAww, 19 October 2012 - 11:43 AM.